1. Field of the Invention
The present invention relates to improvements in an electromagnetic device for cameras.
2. Description of Related Art
One type of known conventional electromagnetic device for cameras is disclosed in Japanese Laid-Open Application No. 64-34621. In addition, the use of elastic adhesives in electromagnetic devices for cameras has been disclosed in Japanese Laid-Open Applications Nos. 61-5766 (which corresponds to U.S. Pat. Nos. 4,205,287) and 60-18803.
An explanation of the device disclosed in Japanese Laid-Open Application No. 64-34621 is provided hereafter, with reference to FIGS. 3 through 5.
In FIG. 3, base plate 1 is provided with arcuate holes 1a and 1b, a shaft 3 and a positioning pin 4 that is fixed to the base plate 1. A yoke 2 is provided with a contact surface 2a, the yoke position being determined by the positioning pin 4, and being mounted on the base plate 1 by means of a fixing screw 5. A coil 6 is wrapped around the yoke 2, and windings 6a and 6b of the coil 6 are connected to a control circuit 7.
FIG. 4 is a cross section of the shaft 3 taken along the line 4--4 in FIG. 3. A cover plate 15, which is essentially parallel to the base plate 1, covers the shaft 3 and extends in a direction parallel to the surface of FIG. 3. The cover plate 15 is not shown in FIG. 3 in order to simplify the drawing. An armature lever 9 is fixed to a shaft bearing 8 so as to be able to rotate around the shaft 3. Pin 12 is fixed to the cover plate 15; one end 10a of a drive spring 10 is attached to the pin 12, while the other end 10b is restrained by a reset pin 16 (see FIG. 3). One end 11a of a reset spring 11 is connected to the bottom of a hole 13a in an armature shaft 13, while the other end 11b is restrained by the reset pin 16.
The armature shaft hole 13a is provided in a catch 13b of the armature shaft 13. The armature shaft 13 is inserted into a hole 9b in the armature lever 9, and is attached to an armature 14. The armature 14 is pushed to the right (in FIG. 3) by one end 11a of the reset spring 11, its contact surface 14a contacting the contact surface 2a of the yoke 2. The armature lever 9 also includes guiding tabs 9e (more clearly shown in FIG. 9) to prevent the armature 14 from rotating relative to armature lever 9. In this instance, the armature lever 9, the reset spring 11, the drive spring 10 and the reset pin 16 correspond to items 154, 157, 156 and 1a, respectively, in FIG. 1 of Japanese Laid-Open Application No. 64-34621.
In FIG. 3, the end 10b of the drive spring 10 and the end 11b of the reset spring 11 both are restrained by the reset pin 16, and because they are not in contact with the bent component 9a of the armature lever 9, no force is applied to the armature lever 9. This enables the armature lever 9 to freely assume a position between the catch 13b and the armature 14. FIG. 3 shows a case where the space between the armature lever 9 and the catch 13b is at a maximum.
Referring to FIG. 5, only those components that differ from FIG. 3 are explained. The FIG. 5 items that are the same as in FIG. 3 are indicated through the attachment of an apostrophe (') to their respective numbers. One end 10b' of the drive spring 10' and one end 11b' of the reset spring 11' are both in contact with the bent component 9a'. The reset pin 16' directly restrains the armature lever 9'. The armature 14' is pressed to the right (in FIG. 5) by the armature lever 9', and its contact surface 14a' contacts the contact surface 2a' of the yoke 2'. Accordingly, in this case the armature lever 9' is restricted to the position shown in FIG. 5 by the reset pin 16' and the armature 14'. In other words, in FIG. 5, the distance between the armature lever 9' and the catch 13b' is forced to its maximum. In this instance, the armature lever 9', the reset spring 11', the drive spring 10' and the reset pin 16' correspond to items 153, 155, 55 and 2b, respectively, in FIG. 1 of Japanese Laid-Open Application No. 64-34621.
As shown in FIG. 3, the armature 14 contacts the yoke 2 when the yoke 2 is excited by the control circuit 7. Subsequently, the reset pin 16 moves in a clockwise direction. The end 10b of the drive spring 10 and the end 11b of the reset spring 11 both rotate in a clockwise direction following the reset pin 16, but eventually come into contact with the bent component 9a.
In the case shown in FIG. 5, the armature 14' contacts to the yoke 2' when the yoke 2' is excited by the control circuit 7'. Subsequently, the reset pin 16' moves in a clockwise direction, but in this case the end 10b' of the drive spring and the end 11b' of the reset spring 11' already are in contact with the bent component 9a'. Because the actions from this point on are the same as in FIG. 3, reference will be made to FIG. 3 in providing further explanation.
The armature lever 9 rotates around the shaft 3 in a clockwise direction under the force of the drive spring 10 and the reset spring 11. When the armature lever 9 rotates by the amount of separation between the catch 13b and the armature 14, the armature lever 9 collides into the catch 13b, in a state shown in FIG. 6. Subsequently, when the yoke 2 is put into an unexcited state by the control circuit 7, the armature 14 rotates around the shaft 3 in a clockwise direction under the driving force of the drive spring 10. Furthermore, the arm 9c presses the pin 17 in a clockwise direction. This state is shown in FIG. 7.
Next, the conventional technology set forth in Japanese Laid-Open Applications Nos. 61-5766 (U.S. Pat. No. 4,205,287) and 60-18803 will be explained with reference to FIG. 8. This technology has a structure wherein an armature 114 is mounted around a shaft 113 that extends parallel to the contact surface 114a so as to be able to rotate. Contact surface 114a contacts the contact surface of a yoke 102. An elastic adhesive is applied as the component E between a bent component 109e of an armature lever 109 and the armature 114. The elastic adhesive E absorbs vibrations of a leaf spring (not shown), also located between bent component 109e and armature 114. This prevents the armature 114 and the yoke 102 from accidently separating when subjected to weak shock forces.
When the conventional technology set forth in Japanese Laid-Open Applications Nos. 61-5766 and 60-18803 and in U.S. Pat. No. 4,205,287 is directly applied to an electromagnetic device having the structure described in Japanese Laid-Open Application No. 64-34621, a number of problems arise, an explanation of which is provided hereafter, with reference to FIG. 9.
FIG. 9 is a drawing of the structure in FIG. 6, modified to incorporate the FIG. 8 technology, viewed in the direction indicated by arrow B in FIG. 6. When the conventional technology set forth in Japanese Laid-Open Applications Nos. 61-5766 and 60-18803 is directly applied to the FIG. 6 structure, the elastic adhesive is applied as components C and D in FIG. 9. In comparing FIGS. 8 and 9, one sees that the difference in structure is that the distance G in FIG. 8 is considerably larger than the distance F in FIG. 9. In the structure in FIG. 9, the contact surface 14a is next to the area of application when the elastic adhesive is applied as components C and D. Accordingly, there is the danger that during the process of applying the elastic adhesive, the elastic adhesive accidentally could be applied to the contact surface 14a.
In addition, generally with this type of electromagnetic device for cameras, there are many cases where the top and bottom are blocked by the base plate 1 and the cover plate 15, so that the task of applying the elastic adhesive must be done in the direction perpendicular to the surface of FIG. 9, with an accompanying reduction in work efficiency. On the other hand, the structure in FIG. 9 also has strong points that should not be eliminated from the design, such as the fact that the entire distance H can be made smaller because the distance F can be reduced.